In automotive manufacturing, lightweight materials, such as aluminum, are used to produce fuel efficient vehicles. Sheet metal components are joined together by welding or by using rivets, such as a self-piercing rivet tool 20 shown in FIGS. 1A-1D during a body-in-white stage in vehicle manufacturing. Referring to FIG. 1A, a self-piercing rivet tool 20 has a nose 22 that surrounds a punch 24. A rivet 26 is carried by the tool 20. The rivet 26 has a tubular body with a tapered end. In FIG. 1B, a self-piercing rivet 26 is shown engaging two panels 28 and 30. The nose 22, punch 24, and rivet 26 are positioned on one side of the panels 28 and 30, and a die 32 is positioned on the opposite side of the panels 28 and 30. Referring to FIG. 1C, the punch 24 drives the rivet 26 into the panels 28 and 30 until the rivet 26 penetrates through the panel 28 into panel 30. The rivet 26 is flared to expand into the bottom panel 30 and the rivet 26 forms a button on the bottom panel 30. Referring to FIG. 1D, the nose 22 and the punch 24 are retracted from the rivet 26. A head 34 of the rivet 26 is flush with the top surface of the top panel 28.
The thickness and the number of panels to be joined by the rivet and the length of the rivet may affect the strength of the interlock provided by the rivet. Where more than two sheets of metal are joined, a rivet may not flare sufficiently. This may result in achieving only a weak interlock between the panels. Adhesives may be used with rivets to improve the strength of the interlock between panels. However, adhesives require time to cure and a weak rivet connection may allow the panels to shift positions before the adhesive cures. Riveting three or more panels together with a single rivet requires a longer rivet. The problem with longer rivets is that they may break through the button in the bottom layer. If the rivet joint is reinforced with adhesive, the adhesive may contaminate the riveting equipment. Production downtime may be incurred for cleaning the riveting equipment.
The above problems and other problems are addressed by this disclosure as summarized below.